Insulation displacement terminals typically comprise at least one insulation displacement contact portion including a slot into which an insulated wire is urged in a direction transverse to the axis of the wire. The slot of the insulation displacement contact includes a portion which is dimensioned and configured to slice through the insulation of the wire as the wire is moving transversely into the slot. The slicing and displacement of the insulation permits edges of the slot below the slicing portion to make electrical contact with the conductors of the wire. Thus, insulation displacement terminals avoid the initial stripping of insulation from the conductor and can avoid the subsequent soldering or crimping of the conductor to the terminal.
The effectiveness of the insulation displacement terminal depends, in part, on the ability of the cantilevered arms of the contact portions to maintain good contact pressure against the conductor. This can be accomplished relatively easily with single strand conductors by merely dimensioning the slot between the cantilevered arms to be a selected distance less than the cross-sectional diameter of the single strand conductor. Thus, upon insertion of the wire into the insulation displacement contact portion, the cantilevered arms of the contact portion will be outwardly deflected by the conductor. The metallic terminal is resilient and designed to respond to the outward deflection elastically. Consequently, outward deflection of the cantilevered arms upon insertion of the wire generates inwardly directed resilient contact forces exerted by the terminal against the conductors for a gripping electrically conductive engagement. These same design theories apply to some wires having multi-strand conductors, and particularly wires having fewer than about twenty strands that have been tightly twisted before the covering insulation is applied.
Recently, electronic and electrical equipment such as household appliances, telecommunications equipment, computers and the like have specified wires employing multi-strand conductors employing a substantially larger number of strands for a given cross-sectional area of the conductor, with the individual strands being of a proportionally smaller cross-sectional dimension. For example, specifications for some high current equipment require wire with a 40 strand conductor defining a total cross-sectional area of 1.25 square mm. Thus, each strand may define a diameter of approximately 0.2 mm. or 0.008 inch. Still other applications envision the use of 100 strand wire where individual strands will approach the thickness of a human hair.
It has been found that the prior art insulation displacement terminals are less effective when used with the above described multi-strand wires having a larger number of strands and with each strand being finer. In particular, it has been found that the strands tend to rearrange substantially upon insertion of the wire into the slot of the insulation displacement terminal presumably at least partly because of the larger number of interstices. This rearrangement of the strands will occur without causing a desired level of outward deflection or the development of the desirable inwardly directed resilient contact forces on the conductors by the cantilevered arms of the prior art insulation displacement terminal. This substantial decrease in deflection and therefore the resilient contact forces or the pressure of the cantilevered arms against the rearranged conductors can result in a significantly poorer quality electrical connection. The ability to develop acceptably high resilient contact forces becomes even more difficult when space limitations effectively reduce the length of the cantilevered arms, thereby reducing the cantilevered moment arm.
The prior art has considered the problem of rearrangement of conductor strands in the context of wires having a comparatively small number of strands. Although many of these prior art structures have been effective for achieving adequate contact pressure for a comparatively small number of strands, they become less effective as the number of strands in the multi-strand wire increases. For example, U.S. Pat. No. 4,317,608 which issued to Dechelette on Mar. 2, 1982 shows an insulation displacement terminal which attempts to address the problem of the rearrangement of strands relative to one another as the wire is urged into the connector. In particular, U.S. Pat. No. 4,317,608 shows an insulation displacement terminal used with wires having between 12 and 18 strands and having a total cross-sectional area of between 0.6-2.0 square millimeters. The slot of the terminal shown in U.S. Pat. No. 4,317,608 includes a pair of opposed convex converging cutting edges which lead to a narrow cutting throat and which then diverge outwardly. These outwardly diverging cutting edges adjacent to the narrow throat terminate at an opposed pair of convex converging noncutting sides which in turn terminate at a generally circular aperture defining the base of the slot. The terminal of U.S. Pat. No. 4,317,608 is designed for the strands of the wire to be disposed generally in the proximity of the narrow throat defined by the converging cutting edges. In particular, the core defined by the strands of the conductor are rearranged longitudinally with respect to the axis of the slot such that a first portion of the strands are disposed between the converging cutting edges and such that a second portion of the strands are disposed adjacent the diverging cutting edges of the terminal. The contact pressure against the strands is provided by the converging cutting edges.
The terminal shown in U.S. Pat. No. 4,317,608 is not sufficiently effective to prevent the rearrangement of the very fine strands described above and thus would not provide sufficient contact pressure against the conductor required in high current applications. Furthermore, the contact pressure exerted by the converging cutting edges could damage the very fine conductor strands now being used.
Another somewhat relevant insulation displacement terminal is shown in U.S. Pat. No. 4,002,391 which issued to Dunn et al on Jan. 11, 1977. The terminal of U.S. Pat. No. 4,002,391 includes a pair of cantilevered arms defining a slot therebetween. The slot includes a narrow wire engaging top portion and an enlarged base portion. One of the cantilevered arms of the terminal is provided with a pair of swages axially spaced from one another along the length of the narrow top portion of the slot. The swages are intended to prevent the single strand wire mounted in the terminal from vibrating out of the slot or into the enlarged base portion of the slot. The two swages on the one arm of the terminal do not affect the degree of contact pressure exerted on the conductor. A similar terminal with a swage for controlling the degree of insertion is shown in U.S. Pat. No. 4,682,835.
The prior art also includes several insulation displacement terminals which rely substantially upon the crimping over of contact arms to achieve the required contact pressure. Examples of such terminals are shown in U.S. Pat. No. 4,159,156 and in U.S. Pat. No. 4,288,918.
An effective prior art insulation displacement terminal is shown in U.S. Pat. No. 4,527,852 which issued to Dechelette on July 9, 1985 and which is assigned to the assignee of the subject invention. The terminal of U.S. Pat. No. 4,527,852 includes a guide portion for guiding the wire including the insulation into a pair of opposed insulation piercing barbs which lead into a narrower cutting portion of the slot. The narrow cutting portion includes protrusions on each side of the slot extending outwardly from the plane of the metal material from which the terminal is made. The protrusions effectively urge the insulation away from the slot to further enhance the quality of the electrical connection. Although the terminal shown in U.S. Pat. No. 4,527,852 has many structural and functional advantages, it is desired to provide a terminal that more positively prevents rearrangement of the strands in a wire having a large number of very fine strands, and to further increase the resilient contact forces exerted upon the conductors by the cantilevered arms of the terminal.
Accordingly, it is an object of the subject invention to provide an insulation displacement terminal effective for use with wires having a large number of fine strands.
It is another object of the subject invention to provide an insulation displacement terminal which provides enhanced contact pressure against the conductors by the cantilevered arms of the terminal.
It is a further object of the subject invention to provide an insulation displacement terminal which relies upon stored energy of deflected contact arms upon the conductors of the wire.
An additional object of the subject invention is to provide an insulation displacement terminal which provides sufficient pressure against the fine conductive strands of a wire to deform the strands and prevent excessive rearrangement of the strands relative to the terminal.
It is another object of the invention to provide an insulation displacement terminal including a contact slot configuration which is effective to restrict downward travel of the wire strands within the slot during insertion to cause a build up in the insertion forces exerted by the wire on the terminal to provide improved deflection of the cantilevered arms and increased resilient contact forces between the arms and the wire strands.
Still another object of the subject invention is to provide an insulation displacement terminal which relies upon stored energy of the contact arms and which enables the contact arms to be crimped over the wire to retain the strands in position.